(a) Technical Field
The present invention relates to a hydrogen supply system for a fuel cell. More particularly, the present invention relates to a hydrogen supply system for a fuel cell which can compensate for a change in temperature caused by heat generated when a high pressure tank is charged and discharged with hydrogen.
(b) Background Art
In general, fuel cells are devices that convert the chemical energy of a fuel directly into electrical energy by an electrochemical reaction without combustion. Such a fuel cell is a zero emission power generation system used as a power source of a vehicle, a power source of a laser apparatus, and the like.
In the fuel cell, a fuel cell stack comprising a fuel cell assembly in which a plurality of unit cells are stacked and other peripheral components generates electricity with hydrogen supplied to an anode as a fuel gas and oxygen supplied to a cathode as an oxidizing agent.
In a fuel cell vehicle, a hydrogen storage tank is mounted for storing hydrogen supplied from a hydrogen fueling station located outside the vehicle and supplying the hydrogen to the fuel cell stack for generation of electricity.
That is, the hydrogen in the fuel cell is first stored in the hydrogen storage tank mounted in the vehicle and then supplied to the fuel cell stack in which the electricity is generated.
Accordingly, it is necessary to recharge the hydrogen storage tank with hydrogen for continuous generation of electricity in the fuel cell stack. The hydrogen fueling station includes a hydrogen supply tank and a compressor. The compressor is operated to increase the pressure of hydrogen from the hydrogen supply tank and the pressurized hydrogen is supplied to the hydrogen storage tank in the vehicle.
Several methods for hydrogen storage are known. For example, hydrogen can be stored as a liquid hydrogen. It can be stored using high pressure compression. Also it can be stored using a hydrogen storage material such as metal hydride, porous nanostructured material, etc.
Among them, the method involving high pressure compression is prevalently used. The method using the hydrogen storage material has been intensively studied.
FIG. 1 is a schematic diagram showing a fuel supply mode according to the high pressure compression method. As shown in FIG. 1, hydrogen supplied from a hydrogen fueling station 1 is charged to a high pressure hydrogen tank 2, and the hydrogen stored in the high pressure hydrogen tank 2 is supplied to a fuel cell stack, if necessary, by regulating the pressure of the hydrogen by means of a high pressure regulator 3 and a low pressure regulator 4.
In this case, a solenoid valve 5 is provided at one end of the high pressure hydrogen tank 2 and an end plug is mounted at the other end such that the hydrogen is charged through the solenoid valve 5, in which a valve thereof is turned on and off by transmitting an operation signal to the solenoid valve 5.
At present, the hydrogen storage method in the fuel cell system compresses the hydrogen gas at high pressure of 350 bar or 700 bar.
However, this method has a drawback in that as it has a low storage density, the compression pressure must be increased at a given volume and/or the storage volume must be increased at a given compression pressure in order to ensure a long driving distance, which is disadvantageous in view of the stability and the limited space of the vehicle.
Moreover, a temperature rise caused by an influence of the pressure when hydrogen is compressed and stored in the high pressure hydrogen tank poses a safety problem.
FIG. 2 is a diagram showing hydrogen absorption and release by a hydrogen storage material. Heat is generated by an exothermic reaction when hydrogen is stored in the hydrogen storage material, and the hydrogen is released when heat is applied from the outside.
However, while the hydrogen storage material has an advantage in that it provides a high hydrogen storage density compared to the high pressure compression method, it is disadvantageous in view of hydrogen absorption and release rate and heat management compared to the high pressure compression method.
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.